In the related art, there is known a parking device which regulates rotation of a driving shaft that drives a wheel to maintain a vehicle in a stopped state when a select lever (shift lever) is selectively operated to a parking range (hereinafter, referred to as a P range). For example, JP-A-05-116540 and JP-A-2009-137427 disclose a parking device of an electric car including: gear-like parking gears which are respectively provided in driving shafts of a driving system that can independently drive left and right wheels; and a parking pawl in which a projected portion that engages with a tooth groove of the parking gears is formed. In the parking device, the projected portion of the parking pawl engages with the tooth groove of the parking gear to regulate the rotation of the driving shaft when a select lever is operated to the P range. Hereinafter, a specific configuration of the driving system described in JP-A-2009-137427 will be described with reference to FIGS. 6 and 7.
As illustrated in FIG. 6, a driving system 100 of JP-A-2009-137427 includes: a left wheel driving system 103A including a first electric motor 101A which drives a left wheel, and a first transmission 102A which is provided on a power transmission path between the first electric motor 101A and the left wheel; a right wheel driving system 103B including a second electric motor 101B which drives a right wheel, and a second transmission 102B which is provided on a power transmission path between the second electric motor 101B and the right wheel; first and second rotation detectors 105A and 105B which are installed on rotor shafts 104A and 104B of each of the electric motors 101A and 101B and detect a rotation angle of each of the rotor shafts 104A and 104B; first and second parking devices 130A and 130B which are installed on each of the rotor shafts 104A and 104B and regulate rotation of each of the rotor shafts 104A and 104B during parking; and a substantially cylindrical case 106 which accommodates these components therein.
As illustrated in FIG. 7, the first and second parking devices 130A and 130B respectively include a parking gear 131, a parking pawl 132, and a parking rod 133. The parking gear 131 has a shape of a gear, and is disposed concentrically to each of the rotor shafts 104A and 104B. A tooth groove 131b which is formed between a tooth 131a and a tooth 131a of the parking gear 131 is configured such that a projected portion 132a of the parking pawl 132 engages therewith.
The parking pawl 132 has the projected portion 132a that engages with the tooth groove 131b at a tip end thereof n addition, a rear end of the parking pawl 132 is rotatably supported by the case 106 via a pawl shaft 134. The pawl shaft 134 is provided with a torsion spring 135 so that a spring load acts in a direction in which engaging between the parking gear 131 and the projected portion 132a of the parking pawl 132 is released. The parking pawl 132 rotates around the pawl shaft 134 by the parking rod 133 when the select lever is selectively operated to the P range.
The parking rod 133 includes a tip end side rod 133a, a rear end side rod 133b, a cam 137, and a coil spring 138. The tip end side rod 133a of the parking rod 133 has a diameter greater than that of the rear end side rod 133b. The tip end side rod 133a is slidably supported by a bracket 136 fixed to the case 106. Meanwhile, on the rear end side rod 133b, the cam 137 for driving the parking pawl 132 is disposed. The cam 137 is slidably provided on the rear end side rod 133b, receives a spring load of the coil spring 138 from the rear part, and abuts against a step 133c formed between the tip end side rod 133a and the rear end side rod 133b. In addition, the rear end side rod 133b is connected to the select lever which is not illustrated at the rear end thereof.
In the above-described first and second parking devices 130A and 130B, when the select lever is selectively operated to the P range, the parking rod 133 moves toward the case 106 side in FIG. 5. When the parking rod 133 moves in this manner, the cam 137 rides on the bracket 136 and pushes up the tip end of the parking pawl 132 from a lower side to an upper side in the drawing. Then, the parking pawl 132 rotates around the pawl shaft 134.
In addition, in a case where the projected portion 132a of the parking pawl 132 abuts against a tooth bottom surface of the tooth groove 131b of the parking gear 131, the projected portion 132a of the parking pawl 132 engages with the tooth groove 131b of the parking gear 131, and thus, the rotation of each of the rotor shafts 104A and 104B is regulated, and the vehicle is maintained in a stopped state.
Meanwhile, in a case where the projected portion 132a of the parking pawl 132 abuts against the tooth tip surface 131c of the parking gear 131, the cam 137 makes the rear end side rod 133b slide toward a side opposite to the case 106 in FIG. 5 against the spring load of the coil spring 138 so as to ensure escape against a stroke of the parking rod 133. Accordingly, it becomes unnecessary for the projected portion 132a of the parking pawl 132 to forcibly press the tip end surface 131c, and this prevents the first and second parking devices 130A and 130B from failing. In a case where the projected portion 132a of the parking pawl 132 abuts against the tooth tip surface 131c in this manner, when the parking gear 131 slightly rotates and the tooth groove 131b of the parking gear 131 comes to a position of the projected portion 132a of the parking pawl 132, the projected portion 132a and the tooth groove 131b engage with each other to regulate the rotation of each of the rotor shafts 104A and 104B, and the vehicle is maintained in a stopped state.
However, in the driving systems of JP-A-05-116540 and JP-A-2009-137427, since two parking devices (parking pawls) are provided, not only there is a concern that the number of components, the costs, the size and the like increase, but also there is a concern that parking effects cannot be sufficiently obtained since there is a case where it is not possible to regulate the rotation of left and right wheels at the same time during a parking operation when phases of the teeth of parking gears of the first and second parking devices are shifted (hereinafter, simply referred to as phases of the left and right parking gears).
Here, the driving system of JP-A-2009-137427 is provided with a phase synchronization unit for synchronizing the phases of the left and right parking gears, and accordingly, it is possible to regulate the rotation of left and right rear wheels at the same time during the parking operation, however, since the phase synchronization unit of JP-A-2009-137427 makes the phases of the left and right parking gears match each other by using a driving force of the electric motor that drives the wheel, when phase-matching the left and right parking gears, there is a concern that power is generated in the wheels, and thereby deteriorating straight traveling performance of the vehicle. In addition, when the phase matching of the parking gears by the phase synchronization unit of JP-A-2009-137427 is executed in a travel stopped state, there is a concern that the vehicle moves, and thus, there is a restriction that the phase matching cannot be executed unless the vehicle is in the middle of traveling.
Meanwhile, in the parking device described in JP-A-05-116540, since teeth of one parking gear of a pair of parking gears are missing in every other tooth, during a selecting operation to the P range, even in a case where the phases of each of the parking gears are shifted, it is possible to engage the parking gear and the projected portion of the parking pawl with each other, however, when the teeth of one parking gear of the pair of parking gears are missing in every other tooth, the tooth groove of the parking gear widens in a gear circumferential direction, and thus, even in a state where the projected portion of the parking pawl engages with the tooth groove of the parking gear, backlash is generated in a rotational direction of the parking gear. Therefore, there is a concern that one wheel rotates during parking only by an amount that corresponds to the tooth groove widened due to teeth missing, and the vehicle moves.